Is Copyscape working properly?

I was building links today and I found 2 articles that I wanted to spin with WordAI. I copied the text, spun it with WordAI and Copyscape didn't find any results. I was happy that I had some really good articles for building links. Then I tried to see what would happen if I just pasted the original article that I found on Google. Guess what? Copyscape didn't find any matches although I pasted the whole damn article directly from Google. Same thing happened with other article - zero results. How?